Deserialization of Untrusted Data Affecting com.fasterxml.jackson.core:jackson-databind package, versions [,2.6.7.5) [2.7.0, 2.8.11.1) [2.9.0, 2.9.5)

com.fasterxml.jackson.core:jackson-databind is a library which contains the general-purpose data-binding functionality and tree-model for Jackson Data Processor.

Affected versions of this package are vulnerable to Deserialization of Untrusted Data. It allows unauthenticated remote code execution because of an incomplete fix for the CVE-2017-7525 deserialization flaw. This is exploitable by sending maliciously crafted JSON input to the readValue method of the ObjectMapper, bypassing a blacklist that is ineffective if the c3p0 libraries are available in the classpath.

Serialization is a process of converting an object into a sequence of bytes which can be persisted to a disk or database or can be sent through streams. The reverse process of creating objects from a sequence of bytes is called deserialization. Deserialization of untrusted data (CWE-502) occurs when an application deserializes untrusted data without sufficiently verifying that the resulting data will be valid, allowing the attacker to control the state or the flow of the execution.

com.fasterxml.jackson.core:jackson-databind allows deserialization of JSON input to Java objects. If an application using this dependency has the ability to deserialize a JSON string from an untrusted source, an attacker could leverage this vulnerability to conduct deserialization attacks.

Exploitation of unsafe deserialization attacks through jackson-databind requires the following prerequisites:

1. The target application allowing JSON user input which is processed by jackson-databind

An application using jackson-databind is only vulnerable if a user-provided JSON data is deserialized.

2. Polymorphic type handling for properties with nominal type are enabled

Polymorphic type handling refers to the addition of enough type information so that the deserializer can instantiate the appropriate subtype of a value. Use of "default typing" is considered dangerous due to the possibility of an untrusted method (gadget) managing to specify a class that is accessible through the class-loader and therefore, exposing a set of methods and/or fields.

3. An exploitable gadget class is available for the attacker to leverage

Gadget chains are specially crafted method sequences that can be created by an attacker in order to change the flow of code execution. These gadgets are often methods introduced by third-party components which an attacker could utilise in order to attack the target application. Not every gadget out there is supported by jackson-databind. The maintainers of jackson-databind proactively blacklists possible serialization gadgets in an attempt to ensure that it is not possible for an attacker to chain gadgets during serialization.

Further reading:

• On Jackson CVEs: Don’t Panic on Medium
• NCC Group Jackson Deserialization WhitePaper
• Java Security Best Practices

• GitHub Commit
• GitHub Issue